Physicians who prescribe opioids for chronic pain are increasingly ordering urine drug tests (UDT) as part of the assessment and follow-up of such patients. The current recommendation is to do such screens initially and then subsequently on a random basis on all such patients. Those of us, like myself, who have been treating some chronic pain patients with opioids for many years have, in the past, obtained UDTs selectively on only those patients whose history or behavior raised some red flags for abuse or addiction potential. Yet physicians who do only selective UDTs may find unexpected results.

In 2007, Michna et al. reported on a retrospective analysis of data from 470 patients who had urine drug testing at a pain management program in an urban teaching hospital.1 They found a 45% incidence of unexpected urine screens. Twenty percent had an illicit substance in their urine. Other abnormalities were the absence of a prescribed opioid or an adulterated urine sample. The only predictive variable for an abnormal UDS was younger age. They observed that common patient descriptors and number, type, or dose of prescribed opioids were poor predictors of abnormal results.

To determine how likely it is that patients in a small private chronic pain practice would have abnormal urine drug tests, all patients on chronic opioids who were seen for routine appointments over a two-month period were asked to submit urine specimens in the office. This article describes the results obtained in this population of 188 patients.

Background

This is a private pain management practice in which medications are prescribed but no invasive procedures carried out. The physician has a background in internal medicine, addiction medicine, and pain management. Most patients are referred by other physicians. At the first visit, a history and physical exam is carried out, including a social and addiction history; procurement of old medical records; and photographing the patients. If patients are to be prescribed opioids, they sign an agreement that specifies the physician’s expectations of the patients:

They will not use illegal drugs

They will not change their dose without prior discussion with the physician

They will not obtain scheduled substances from another provider without notifying the pain physician

They will get their prescriptions filled at a single pharmacy (of their choosing)

They will obtain consultations or go to physical therapy if asked to

They will not be given early refills if the medications are used up early or are lost or stolen

They will give a urine specimen for drug testing if asked

Breaches of the agreement are evaluated on a case-by-case basis.

The patients have a wide variety of chronic non-cancer pain with back pain being the most common diagnosis in the practice. Many of the patients have undergone surgery or other invasive procedures and are still in significant pain. They are informed early on that the physician will work with them if they have other issues such as addiction, but that lying to the physician is likely to get them discharged. Stable patients are typically seen once every two months. Most patients on opioids are given both sustained-release and break-through pain medication.

Methods

In March and April of 2007, every patient coming in for a routine or urgent exam or consultation was asked to submit a urine specimen. Although all had given permission to do this as part of the opioid agreement they signed when first seen, many had not been tested in a long time and were not expecting it. Some long-term patients had not had an initial urine drug test (UDT). The patients were not observed urinating, but the medical assistant checked the temperature of the freshly voided urine as shown on a liquid crystal thermometer on the side of the cup, to assure it was within the range of 90 to 100 degrees Fahrenheit. Specific gravity measurements were not done. The patients were asked when they had last taken each of their opioid medications. The urine specimens were sent to a local laboratory where they were screened by enzyme immunoassay (EIA) using the lab’s “routine” urine drug screen which included the usual drugs of abuse—alcohol, amphetamines, cannabinoids, cocaine, and phencyclidine—plus opiates, benzodiazepines, barbiturates, and propoxyphene, as well as whatever scheduled drugs the patient was being prescribed. Immunoassays have limitations regarding sensitivity and specificity. The immunoassay used by this laboratory employed an Olympus 2700 machine and Syva reagents, when available, along with Microgenics reagents for oxycodone and oxymorphone. Positive results were confirmed using a gas chromatography-mass spectrometry (GC/MS) test, which also provided a quantitative determination.

A total of 188 patients were screened. Their mean age was 53.8 years ± 11.64, with an age range of 23 to 91. The results were classified as expected or unexpected. “Unexpected” results—found in 29 patients (15.4%)—were those in which the urine: (1) contained illicit substances, (2) contained another non-prescribed opioid, and/or (3) did not contain a prescribed opioid. Whenever an unexpected result was obtained, the patient was questioned for an explanation. For example, two patients had amphetamines in their urine because they were being prescribed these drugs by a psychiatrist. In another case, a urine that screened positive for amphetamines was in fact negative on GC/MS. In yet another case, the patient had not taken a breakthrough pain medication in the past 12 hours but had mistakenly told us initially that she had taken both the long-acting and the short-acting that morning. If we were uncertain whether an unexpected result could reflect a metabolite of a prescribed drug, the laboratory was consulted.

Clinicians who order urine drug tests need to understand the various types of urine tests and what they can or cannot do. Standard screening tests report only whether various classes of drugs are present or absent based on an arbitrary cut-off level. If a member of the drug class, (for example, opiates or benzodiazepines) is present in a quantity below the cut-off, the test is reported as negative. This is why it is a good idea to ask, at the time of testing, what time the patient last took any of the drugs being tested. The standard immunoassay reacts only with natural opiates (such as morphine, hydrocodone, hydromorphone, and codeine). This test is likely to miss semi-synthetic and synthetic opioids (such as fentanyl, oxycodone, and oxymorphone), although very high doses of semisynthetic opioids (e.g., oxycodone) may be picked up on the immunoassay. To identify specific drugs and their concentration in the urine, labs offer gas chromatography/ mass spectrometry (GC/MS) or high-performance liquid chromatography (HPLC). Unexpected positive and negative immunoassay results should be confirmed by one of these more specific techniques.

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